Indwelling ureteral catheter stents or drainage tubes have been used to bypass ureteral obstructions or ureterovaginal fistulas and maintain urinary drainage. In the past, stents made of open end silicone tubing have been used for this purpose and have provided good drainage for sustained periods of time. However, the use of such open end tubing has not been completely satisfactory. For example, in some instances, the tubing has migrated and in others it has been expelled. In still other instances, the lumen of the tubing has become encrusted greatly reducing urinary drainage.
Various attempts have been made to produce stents which do not have the problems which accompany the use of open end tubing. For example, stents have been designed which are closed at one end to facilitate passage into a body passage and which have radial passageways in the wall connecting the lumen to the outside and a flange at the other end to make upward migration of the stent less likely. Another approach to prevent migration has been to provide the body of the stent with sharply pointed barbs which are designed to prevent downward migration and explusion. However, such barbs increase the diameter of the stent making it more difficult to insert and in some instances can cause the stent to migrate outside the bladder to create medical or other problems for the urologist. Recently, a stent has been introduced which is made of stiff polyethylene. It has a relatively small flange on the distal end which is intended to prevent upward migration, and the proximal end is formed in the shape of a pigtail. Unfortunately, this stent must be introduced by the relatively complex Seldinger technique. Furthermore, the relatively small flange has not always prevented the stent from passing above the bladder making removal uncertain.
All the prior art stents have one feature in common; they are primarily designed to be passed endoscopically in a retrograde fashion and not during open surgery.
The ideal ureteral stent should have at least the following desirable characteristics: (1) The stent should be made of a material which is soft, quite flexible and resists tissue reaction and encrustation; (2) it should be radiopaque; (3) to facilitate its passage it should be of a uniform diameter throughout without barbs or flanges; (4) it should be easily passed during open surgery as well as endoscopically; (5) it should have means to prevent migration in either direction; and (6) it should be able to withstand repeated sterilization. It also would be desirable if the stent would be of a design which resists plugging of flow due to encrustation.
In my earlier patent application, Ser. No. 844,278, filed Apr. 7, 1978, I disclosed an improved ureteral stent having a hook at each end to prevent migration. This stent has proven to be a significant advance in the art of ureteral stents in that it does not migrate and it resists encrustation extremely well in noninfected urine, especially when the stent is formed of a silicone elastomer. However, even such stents of silicone elastomer can become encrusted with various materials found in urine in the presence of infections.
Certain bacteria which commonly cause urinary tract infections (proteus and pseudomonas) can cause severe encrustation. These organisms produce an enzyme which can break down urea, a normal component of all urine into ammonia. Therefore, they are called "urea splitting" bacteria. Ammonia makes the normally acid urine highly alkaline. As the calcium salts in the urine are much more soluble and are often near saturation in the normal acid urine, these salts, especially calcium phosphate, precipitate out in the alkaline urine caused by the urea splitting organisms. In the face of a urinary tract infection, the stents may have calcium phosphate encrusted within, which completely obstructs the lumen of the stent thus interfering with urinary drainage.